Activation of tumor necrosis factor receptor 1 in airway smooth muscle: a potential pathway that modulates bronchial hyper-responsiveness in asthma?

The cellular and molecular mechanisms that are involved in airway hyper-responsiveness are unclear. Current studies suggest that tumor necrosis factor (TNF)-α, a cytokine that is produced in considerable quantities in asthmatic airways, may potentially be involved in the development of bronchial hyper-responsiveness by directly altering the contractile properties of the airway smooth muscle (ASM). The underlying mechanisms are not known, but growing evidence now suggests that most of the biologic effects of TNF-α on ASM are mediated by the p55 receptor or tumor necrosis factor receptor (TNFR)1. In addition, activation of TNFR1 coupled to the tumor necrosis factor receptor-associated factor (TRAF)2-nuclear factor-κB (NF-κB) pathway alters calcium homeostasis in ASM, which appears to be a new potential mechanism underlying ASM hyper-responsiveness

Tissue specific expression of human fatty acid oxidation enzyme genes in late pregnancy

Background: Abnormal fatty acid oxidation (FAO) is associated with maternal and fetal complications during pregnancy. The contribution of maternal and fetal tissues to FAO capacity during late pregnancy is important to understand the pathophysiology of pregnancy-associated complications. The aim of this study was to determine the expression levels of mitochondrial FAO enzymes in maternal and fetal tissues during late normal pregnancy. Methods: We have measured by Real-time PCR the levels of long- and medium -chain acyl-CoA dehydrogenase (LCHAD and MCAD), two acyl-CoA dehydrogenases that catalyze the initial step in the mitochondrial FAO spiral. Results: LCHAD and MCAD were expressed in maternal skeletal muscle, subcutaneous adipose tissue, placenta, and maternal and fetal blood cells. LCHAD gene expression was four- to 16-fold higher than MCAD gene expression in placenta, adipose tissue and skeletal muscle. In contrast, MCAD gene expression was ~5-fold higher in fetal blood than maternal blood (p = 0.02), whereas LCHAD gene expression was similar between fetal blood and maternal blood (p =0.91). Conclusions: LCHAD and MCAD are differentially expressed in maternal and fetal tissues during normal late pregnancy, which may represent a metabolic adaptation in response to physiological maternal dyslipidemia during late pregnancy.Consejeria de Salud, Junta de Andalucía Num Expte: 0269/05

Per-arnt-sim (PAS) domain-containing protein kinase is downregulated in human islets in type 2 diabetes and regulates glucagon secretion.

AIMS/HYPOTHESIS: We assessed whether per-arnt-sim (PAS) domain-containing protein kinase (PASK) is involved in the regulation of glucagon secretion. METHODS: mRNA levels were measured in islets by quantitative PCR and in pancreatic beta cells obtained by laser capture microdissection. Glucose tolerance, plasma hormone levels and islet hormone secretion were analysed in C57BL/6 Pask homozygote knockout mice (Pask-/-) and control littermates. Alpha-TC1-9 cells, human islets or cultured E13.5 rat pancreatic epithelia were transduced with anti-Pask or control small interfering RNAs, or with adenoviruses encoding enhanced green fluorescent protein or PASK. RESULTS: PASK expression was significantly lower in islets from human type 2 diabetic than control participants. PASK mRNA was present in alpha and beta cells from mouse islets. In Pask-/- mice, fasted blood glucose and plasma glucagon levels were 25 ± 5% and 50 ± 8% (mean ± SE) higher, respectively, than in control mice. At inhibitory glucose concentrations (10 mmol/l), islets from Pask-/- mice secreted 2.04 ± 0.2-fold (p < 0.01) more glucagon and 2.63 ± 0.3-fold (p < 0.01) less insulin than wild-type islets. Glucose failed to inhibit glucagon secretion from PASK-depleted alpha-TC1-9 cells, whereas PASK overexpression inhibited glucagon secretion from these cells and human islets. Extracellular insulin (20 nmol/l) inhibited glucagon secretion from control and PASK-deficient alpha-TC1-9 cells. PASK-depleted alpha-TC1-9 cells and pancreatic embryonic explants displayed increased expression of the preproglucagon (Gcg) and AMP-activated protein kinase (AMPK)-alpha2 (Prkaa2) genes, implying a possible role for AMPK-alpha2 downstream of PASK in the control of glucagon gene expression and release. CONCLUSIONS/INTERPRETATION: PASK is involved in the regulation of glucagon secretion by glucose and may be a useful target for the treatment of type 2 diabetes

Mechanism of cloned ATP-sensitive potassium channel activation by oleoyl-CoA.

Insulin secretion from pancreatic beta cells is coupled to cell metabolism through closure of ATP-sensitive potassium (KATP) channels, which comprise Kir6.2 and sulfonylurea receptor (SUR1) subunits. Although metabolic regulation of KATP channel activity is believed to be mediated principally by the adenine nucleotides, other metabolic intermediates, including long chain acyl-CoA esters, may also be involved. We recorded macroscopic and single-channel currents from Xenopus oocytes expressing either Kir6.2/SUR1 or Kir6. 2DeltaC36 (which forms channels in the absence of SUR1). Oleoyl-CoA (1 microM) activated both wild-type Kir6.2/SUR1 and Kir6.2DeltaC36 macroscopic currents, approximately 2-fold, by increasing the number and open probability of Kir6.2/SUR1 and Kir6.2DeltaC36 channels. It was ineffective on the related Kir subunit Kir1.1a. Oleoyl-CoA also impaired channel inhibition by ATP, increasing the Ki values for both Kir6.2/SUR1 and Kir6.2DeltaC36 currents by approximately 3-fold. Our results indicate that activation of KATP channels by oleoyl-CoA results from an interaction with the Kir6.2 subunit, unlike the stimulatory effects of MgADP and diazoxide which are mediated through SUR1. The increased activity and reduced ATP sensitivity of KATP channels by oleoyl-CoA might contribute to the impaired insulin secretion observed in non-insulin-dependent diabetes mellitus

Long-chain CoA esters activate human pancreatic beta-cell KATP channels: potential role in Type 2 diabetes.

AIMS/HYPOTHESIS: The ATP-regulated potassium (KATP) channel in the pancreatic beta cell couples the metabolic state to electrical activity. The primary regulator of the KATP channel is generally accepted to be changes in ATP/ADP ratio, where ATP inhibits and ADP activates channel activity. Recently, we showed that long-chain CoA (LC-CoA) esters form a new class of potent KATP channel activators in rodents, as studied in inside-out patches. METHODS: In this study we have investigated the effects of LC-CoA esters in human pancreatic beta cells using the inside-out and whole-cell configurations of the patch clamp technique. RESULTS: Human KATP channels were potently activated by acyl-CoA esters with a chain length exceeding 12 carbons. Activation by LC-CoA esters did not require the presence of Mg2+ or adenine nucleotides. A detailed characterization of the concentration-dependent relationship showed an EC50 of 0.7+/-0.1 micromol/l. Furthermore, in the presence of an ATP/ADP ratio of 10 (1.1 mmol/l total adenine nucleotides), whole-cell KATP channel currents increased approximately six-fold following addition of 1 micro mol/l LC-CoA ester. The presence of 1 micro mol/l LC-CoA in the recording pipette solution increased beta-cell input conductance, from 0.5+/-0.2 nS to 2.5+/-1.3 nS. CONCLUSION/INTERPRETATION: Taken together, these results show that LC-CoA esters are potent activators of the KATP channel in human pancreatic beta cells. The fact that LC-CoA esters also stimulate KATP channel activity recorded in the whole-cell configuration, points to the ability of these compounds to have an important modulatory role of human beta-cell electrical activity under both physiological and pathophysiological conditions